An elevator system typically includes a car, a frame, roller guide assembly, and guide rails mounted in a hoistway. The car and roller guide assembly are mounted on the frame. The car and frame move along the guide rails with the movement of roller guide assembly.
Vibration in elevator systems are due to many sources, such as deformation of the guide rails, aerodynamic forces, and passenger load. This invention is particularly concerned with reducing lateral vibration induced by a distortion or misalignment of the guide rails. When the elevator moves sufficiently fast, level variation or winding of the guide rails can induce significant lateral movements of the frame and the car, which lead to discomfortness for the riders. Better ride quality usually imposes higher requirement on the installation of guide rails, and thus increase the cost of installation and maintenance. Tradeoffs have to be made between the system cost and the ride comfort during the design of an elevator system.
A conventional passive vibration reduction system of an elevator includes springs and rubbers, whose parameters, i.e., stiffness and damping coefficients, are fixed and designed according to a selected performance index and an intended operation situation. The passive design suffers either undesirable ride quality or stringent installation accuracy of guide rails. To improve the ride comfort, fully active vibration devices were developed to allow the versatility of suspension forces reacting to the vibration. Due to its capability to track the reference force, which is computed by a controller to meet higher ride quality, a fully active actuator can attenuate the vibration better. For instance, prior work disclosed an active vibration reduction device using an electromagnetic actuator U.S. Pat. No. 7,007,774. Since the active actuator can remove or transfer energy to elevator system, the durability and the cost of a fully active vibration reduction system are major concerns, albeit it can provide desirable performance on the vibration attenuation.
To provide a better trade-off between cost and performance, semi-active vibration reduction devices are known in the art. A semi-active actuator, which allows for the adjustment of actuator parameter, such as viscous damping coefficient or stiffness, is employed to achieve the majority of performance as the fully active actuator does but at a lower cost and improved reliability. In fact, the resultant semi-active system is reliable because it can only dissipate energy.
Work on the lateral vibration reduction of elevators using semi-active actuators includes a hydraulic damper where the damping coefficient is adjusted by controlling the movable orifice lever in a solenoid U.S. Pat. No. 5,289,902. Another system uses a vibration damping device, which is installed between car and frame, and whose damping coefficient can be adjusted according to the elevator speed. Scheduling the damping coefficient merely on the elevator speed limits the effectiveness of attenuating the vibration, U.S. 2009/0308696.
There is a guide roller, whose hardness can be changed with respect to speed of rotation of the roller, by including magnetorheological fluids in the roller. Due to the absence of control mechanism, the achievable performance might be limited, U.S. 2009/0294222. The uses of semi-active actuators with variable stiffness are also described U.S. 2006/0207835, and U.S. 2007/0000732.